1. Field of the Invention
The present invention relates to an electrical connector assembly which comprises an electrical connector and a pick up cap, the pick up cap being mounted to the connector for providing a plane top surface to be engaged by a vacuum suction device, whereby the connector assembly can be moved onto a circuit substrate such as a printed circuit board (PCB) on which the connector is to be mounted.
2. Description of the Related Art
On many production lines, electronic components such as electrical connectors are mounted onto circuit substrates such as printed circuit boards (PCBs) by surface mount technology (SMT), as disclosed in U.S. Pat. Nos. 5,615,477 and 4,916,805.
A method of mounting an electrical connector onto a PCB by SMT generally comprises a sequence of the following steps A through F:    A—Application of an adhesive film on the PCB having a plurality of metal contact pads. The application of the adhesive film may be performed by screen printing, pin transfer, or from a dispenser onto predetermined areas of the PCB.    B—Activation of the adhesive film by irradiation with actinic light in the ultraviolet (UV) or visible wavelength range between 200 and 600 nm, to a degree and for a period of time such that a desired initial tackiness is produced.    C—Mounting the connector with its contacts on the activated adhesive film and the metal contact pads of the PCB.    D—Curing the adhesive film at a temperature between 60˜140° C.; for example, in a convection cabinet, using infrared radiant heaters or by means of the actinic radiation source used in step B if such source also produces infrared radiation.    E—Producing electrical engagement between the contacts of the connector and the corresponding metal contact pads of the PCB by soldering in a wave solder machine or in drag soldering equipment;    F—Cooling the assembly to room temperature.
In step C, the connector is accurately positioned on the PCB by means of a vacuum suction device. Generally, a typical connector has a multiplicity of holes in a flat top portion thereof. Thus the connector does not have a suitably smooth, integral top surface for engagement by a vacuum suction device. Typically, a pick up cap is attached on the top portion of the connector to provide the required plane top surface. Such pick up caps are disclosed in U.S. Pat. Nos. 6,413,111, 6,478,588, 6,533,592, 6,547,609, 6,561,825 and 6,572,383.
FIG. 6 is an isometric view of a related pick up cap 9 used in an land grid array (LGA) connector 8. The connector 8 comprises a generally rectangular insulative housing 81, a plurality of electrical contacts 82 received in the housing 81, a metal stiffener 83 partly covering and reinforcing the housing 81, a lever 84 pivotably received in an end of the stiffener 83, and a metal clip 85 pivotably mounted to an opposite end of the stiffener 83 for engaging with the lever 84. The pick up cap 9 has a substantially rectangular body portion 91. The body portion 91 has a plane top surface 910, and a bottom surface 911 opposite to the top surface 910. A pair of first clasps 92 is formed at opposite sides of a front end of the body portion 91 respectively, and a pair of spaced second clasps (not shown) is formed at a middle portion of a rear end of the body portion 91. Also referring to FIG. 7, the first clasps 92 and the second clasps snappingly clasp corresponding edges of the clip 85 of the connector 8. The pick up cap 9 is thereby securely mounted onto the connector. In this position, a vacuum suction device (not shown) can engage the top surface 910 of the pick up cap 9. The connector 8 can thus be moved to a desired location on a PCB (not shown), with the contacts 82 of the connector 8 engaged on an activated adhesive film and metal contact pads of the PCB. The contacts 82 are then soldered to the metal contact pads. When the entire assembly has cooled, the pick up cap 9 is detached from the connector 8. An electronic package such as an LGA central processing unit (CPU) (not shown) can then be mounted onto the connector 8. The connector 8 enables electrical connection between the CPU and the PCB.
However, the pick up cap 9 and the stiffener 83 cover the connector 8. When curing the adhesive film at high temperature in a convection cabinet using infrared radiant heaters, heated air can only flow through a gap between the top portion of the connector 8 and the clip 85 to a bottom portion of the connector 8. Generally, the time needed for curing the adhesive film is short. Thus, the adhesive film is liable to cure non-uniformly. When this happens, electrical engagement between some of the contacts 82 and the corresponding metal contact pads of the PCB may be flawed. The connector 8 may not reliably electrically connector the CPU and the PCB. Additionally, when cooling the entire assembly to room temperature, heated air can only be dissipated out through the gap between the top portion of the connector 8 and the clip 85. This increases the time needed for cooling the assembly, which reduces the efficiency of mounting of the connector 8 onto the PCB.
In view of the above, a new pick up cap that overcomes the above-mentioned disadvantages is desired.